Uniform stress needle

ABSTRACT

A linear surgical needle is provided having a body portion including a proximal end section; a central section; and a distal end section. The distal end section has a substantially parabolic configuration for producing a substantially uniform stress profile along a length thereof.

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure claims the benefit of and priority to U.S.Provisional Patent Application Ser. No. 60/396,376, filed on Jul. 17,2002, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to surgical needles and, moreparticularly to surgical needles having a distal taper exhibiting asubstantially uniform stress profile which is resistant to a bendingload applied thereto.

BACKGROUND OF RELATED ART

Surgical suture needles are well known in the medical arts and includeprimarily two types of needles, taper point type needles and cuttingedge type needles. A taper point type surgical needle includes aproximal end portion defining a suture-mounting portion having a hole orchannel to which a suture is to be attached, an intermediate portiondefining a main body portion having a generally uniform cross-sectionalarea throughout an entire length thereof and a distal end portiondefining a tapered portion whose cross-sectional area decreasesprogressively toward a pointed distal end of the suture needle. Cuttingedge type needles also taper to a piercing point, however, unlike taperpoint type needles, cutting edge type needles include one or morecutting edges with an otherwise smooth outer surface.

In the design of either taper point type or cutting edge type surgicalneedles it is generally desirable for the needles to exhibit favorablestrength and ease of penetration characteristics. It is desirable for asurgical needle to be sufficiently strong in order to penetrate tissuewhich is being sutured without bending or breaking during a surgicalprocedure. It is also desirable for the surgical needle to easilypenetrate and smoothly pass through the tissue being sutured. The amountof force required for the surgical needle to penetrate tissue includesthe force required for the engagement of the tip of the needle with thetissue and the subsequent creation of the entry hole as well as theforce required for the widening of the entry hole created. The forcerequired for a taper point type surgical needle to widen the hole isgreater than the force required for a cutting edge type needle since thetaper point type needle merely dilates the hole and does not cut thehole as would a cutting edge type needle.

Taper point type surgical needles typically have a taper from a middlesection of the needle body which ends in a distal piercing point. Thetaper is often expressed as a ratio of the length of the taper sectionto the diameter of the wire used to form the needle. It is known thatthe higher the taper ratio is, the more slender the taper, and thus theresistance to penetration and/or piercing through tissue will typicallybe lessened. However, the more slender the taper, the mechanicalstrength for needles manufactured from the same material will belessened. The converse is also to be expected for needles having lowertaper ratios.

In practice, the piercing resistance which the suture needle receivesfrom the tissue of the living body is at a maximum level when thesurgical needle is first piercing the skin of the tissue. This is due tothe fact that the skin of the tissue has a greater rupture strength thanthe other parts or layers of the tissue. The resistance of the sutureneedle as the needle pierces through the skin of the tissue greatlydepends on the degree of sharpness of the pointed end of the sutureneedle. Once the suture needle pierces the skin of the tissue, thepiercing resistance is abruptly reduced regardless of the value of thecross-sectional area increase rate of the tapered portion.

In view of the above, it is apparent that the design techniquesgenerally employed to meet the above two design criteria of strength andease of penetration are often in conflict. As stated above, one approachto improve the strength of a needle is to increase the diameter orthickness of the needle. However, by increasing the thickness of theneedle, the force necessary to penetrate the tissue is also increased,and the opening left in the tissue after passage of the needle is alsoenlarged. Similarly, ease of penetration can be improved by making theneedle thinner or more slender. However, a reduction in the thickness ofthe needle will generally result in a corresponding reduction in thestrength of the needle. Thus the design of a needle which exhibitsfavorable strength and penetration characteristics requires that certaintradeoffs be made in the two criteria to arrive at a needle with optimaloverall performance.

Accordingly, there is a continuing need for surgical tapered needlesexhibiting improved penetrating characteristics (i.e., resistance topenetration through tissue) and improved mechanical characteristics suchas bending strength.

SUMMARY

The present disclosure is directed to a surgical needle having a distalend taper or parabolic profile which exhibits a substantially uniformstress profile when subjected to a load to resist bending thereof.

The surgical needle is intended for use in suturing delicate tissue inconjunction with a plastic, ophthalmologic or reconstructive surgicalprocedure. The surgical needle includes a taper point profile designedto function as a uniform stress beam and resist bending loads applied tothe needle end. The taper point profile is defined by havingcross-section diameters which dynamically increase over the length ofthe needle end. More specifically, the taper point profile of theuniform stress type needle defmes a varied taper angle along the lengthof the needle end with the taper angle decreasing at locations away fromthe needle point. The taper angles, particularly, adjacent the needleend of the uniform stress type needle are typically substantiallygreater than corresponding taper angles of a conventional continuoustaper point type needle. Thus, the uniform stress type needle defines anenlarged taper point profile relative to conventional taper point typeneedles. Consequently, the uniform stress type needle is desirably moreresistant to breakage.

The cross-section diameters of the taper point profile of the uniformstress type needle are calculated at distances from the needle pointusing a predetermined maximum allowable stress value. The formulaemployed for calculating section diameters of the taper point profile isderived from the universal formula for bending stress in a tip loadedcantilever beam The bending stress at a location along a cantilever beamis directly related to the bending moment and sectional properties atthe particular location. Diameters are calculated as a function of themaximum allowable bending stress and the distance from the needle pointat specific locations along the taper point profile. The formula for thedesired maximum bending stress for circular section properties, and theformula for the bending moment are combined into a formula defining thediameters along the length of a tip loaded round section tapering beam.The resulting formula is as follows:d ³=[(32W)/(πσ)]*(X _(n))where

-   -   d=measured diameter at location X_(n);    -   W=load normal to the needle;    -   X_(a)=distance from a distal-most end of the needle; and    -   σ=chosen stress restraint.

The various diameters calculated create a taper point profile whicheffectively functions as a uniform stress beam. An exception is made inthe area or region up to one wire diameter from the needle point topermit a sharper tip angle.

According to one aspect of the present disclosure, a surgical needle isprovided having a linear body portion including a proximal end section;a central section; and a distal end section. The distal end section hasa substantially parabolic configuration for producing a substantiallyuniform stress profile along a length thereof. Preferably, the distalend section has a diameter determined according to the equation providedabove.

In certain embodiments, the distal end section includes a distal tiphaving a uniform taper. The distal tip can have a length which issubstantially equal to a diameter of the central section of the surgicalneedle.

It is envisioned that the proximal end section is configured and adaptedto secure a suture thereto. The central section can have a rectilinear,circular, oval, triangular, I-beam and/or ribbon shaped cross-sectionalprofile.

According to another aspect of the present disclosure, a uniform stressneedle is provided. The uniform stress needle includes a proximal endsection configured and adapted to secure a suture thereto; a centralsection having a uniform transverse cross-sectional profile; and adistal end section having a parabolic surface profile for producing asubstantially uniform stress along a length thereof. Preferably, thesurface profile of the distal end section is defined by the equationprovided above.

It is envisioned that the distal end section includes a distal tiphaving a uniform taper. The distal tip preferably has a length which issubstantially equal to a diameter of the central section of the needle.

According to yet another embodiment of the present disclosure, asurgical needle is provided including a body portion having a proximalend section; a central section; and a distal end section. The distal endsection has a substantially parabolic configuration for producing asubstantially uniform stress profile along a length thereof. The distalend section includes a distal tip having a uniform taper.

These and other objects will be more clearly illustrated below by thedescription of the drawings and the detailed description of thepreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a perspective view of a surgical needle in accordance with thepresent invention;

FIG. 2 is a side elevational view of a distal end of the surgical needleshown in FIG. 1;

FIG. 3 is a schematic side elevational view of the surgical needle shownin FIG. 1 illustrated as a cantilevered beam; and

FIG. 4 is a schematic side elevational view of the surgical needle shownin FIG. 1 illustrating the application of a load force at a distal endthereof

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the presently disclosed surgical needle willnow be described in detail with reference to the drawing figures whereinlike reference numerals identify similar or identical elements. As usedherein, the term “distal” refers to that portion which is further fromthe user, while the term “proximal” refers to that portion which iscloser to the user.

Referring now in detail to FIGS. 1-4, a surgical needle in accordancewith the present invention is generally designated with the referencenumeral 100. Surgical needle 100 includes a linear body portion 102having a proximal end section 110, a distal end section 120 and acentral section 130. Although FIG. 1 illustrates a straight point typesurgical needle, it will be appreciated by those skilled in the art thatsurgical needle 100 may have other conventional curvatures includingcompound, ¼, ⅜, ½ or ⅝ type curvatures.

It will be appreciated by those skilled in the art that proximal endsection 110 is configured and adapted to receive and hold a surgicalsuture 112 therein or therethrough. While central section 130 is shownas having a generally rectangular and/or rectilinear cross-section, itis contemplated that central section 130 may have other conventionalconfigurations including circular, oval, triangular, I-beam, ribbon andthe like. The cross-sectional profile should be such that a conventionalneedle grasper can sufficiently grasp and effectively maintain surgicalneedle 100 in a fixed position as surgical needle 100 penetrates bodytissue, thereby preventing the needle from slipping between the jaws ofthe needle grasper. It is contemplated that central section 130 has auniform transverse cross-sectional profile.

Referring now to FIGS. 24, distal end section 120 of surgical needle 100has a substantially parabolic surface profile for producing asubstantially uniform stress profile along its length. The parabolicsurface profile of distal end section 120 is determined using knownengineering principles. Accordingly, the resulting formula for thecross-sectional diameter of distal end section 120 of surgical needle100 is as follows:d=(((32W)/(πσ))*(X _(n)))ˆ(⅓)where

-   -   d=measured diameter at location X_(n);    -   W=load normal to the needle;    -   X_(n)=distance from a distal-most end of the needle; and    -   =chosen stress restraint.

Thus, in accordance with the present disclosure, in a preferredembodiment, the longitudinal cross-sectional profile of distal endsection 120 of surgical needle 100 will exhibit a curvature defined bythe diametrical equation above. Accordingly, by manufacturing distal endsection 120 of surgical needle 100 in accordance with the abovediametric equation, distal end section 120 of surgical needle 100 willexperience a substantially uniform stress profile along its length.

In other words, as a load, weight and/or force “W” acts on distal endsection 120 of needle 100, as seen in FIGS. 2-4, distal end section 120experiences a substantially uniform stress at each location X_(n) alongits length thereby defining a substantially uniform stress profile alongits entire length thereof.

EXAMPLE

Assuming the following:

-   -   Length of the distal end section of the surgical needle=0.3        inches;    -   Stress=σ=145,000 p.s.i.; and    -   Tip Load=W=35 grams at 45° or 0.077 lbs at 45°.

Selected exemplative calculated diameters for the distal end section ofthe surgical needle appear in the following table. Distance from TipDistance from Tail Diameter 0.001 0.299 0.0015548 0.002 0.298 0.00195890.003 0.297 0.0022424 0.004 0.296 0.0024681 0.005 0.295 0.0026587 0.0060.294 0.0028253 0.007 0.293 0.0029742 0.008 0.292 0.0031096 0.009 0.2910.0032341 0.010 0.290 0.0033497 0.011 0.289 0.0034579 0.012 0.2880.0035596 0.013 0.287 0.0036559 0.014 0.286 0.0037473 0.015 0.2850.0038345 0.016 0.284 0.0039179 0.017 0.283 0.0039978 0.018 0.2820.0040747 0.019 0.281 0.0041488 0.020 0.280 0.0042204 0.021 0.2790.0042896 0.022 0.278 0.0043566 0.023 0.277 0.0044217 0.024 0.2760.0044848 0.025 0.275 0.0045463 0.026 0.274 0.0046061 0.027 0.2730.0046644 0.028 0.272 0.0047213 0.029 0.271 0.0047769 0.030 0.2700.0048311 0.031 0.269 0.0048842 0.032 0.268 0.0049362 0.033 0.2670.0049871 0.034 0.266 0.0050370 0.035 0.265 0.0050859 0.036 0.2640.0051339 0.037 0.263 0.0051810 0.038 0.262 0.0052272 0.039 0.2610.0052727 0.040 0.260 0.0053174 0.041 0.259 0.0053613 0.042 0.2580.0054045 0.043 0.257 0.0054471 0.044 0.256 0.0054890 0.045 0.2550.0055303 0.046 0.254 0.0055709 0.047 0.253 0.0056110 0.048 0.2520.0056505 0.049 0.251 0.0056895 0.050 0.250 0.0057280 0.051 0.2490.0057659 0.052 0.248 0.0058033 0.053 0.247 0.0058403 0.054 0.2460.0058768 0.055 0.245 0.0059129 0.056 0.244 0.0059485 0.057 0.2430.0059837 0.058 0.242 0.0060185 0.059 0.241 0.0060529 0.060 0.2400.0060869 0.061 0.239 0.0061205 0.062 0.238 0.0061538 0.063 0.2370.0061867 0.064 0.236 0.0062192 0.065 0.235 0.0062514 0.066 0.2340.0062833 0.067 0.233 0.0063149 0.068 0.232 0.0063462 0.069 0.2310.0063771 0.070 0.230 0.0064078 0.071 0.229 0.0064382 0.072 0.2280.0064683 0.073 0.227 0.0064981 0.074 0.226 0.0065276 0.075 0.2250.0065569 0.076 0.224 0.0065859 0.077 0.223 0.0066146 0.078 0.2220.0066432 0.079 0.221 0.0066714 0.080 0.220 0.0066995 0.081 0.2190.0067273 0.082 0.218 0.0067548 0.083 0.217 0.0067822 0.084 0.2160.0068093 0.085 0.215 0.0068362 0.086 0.214 0.0068629 0.087 0.2130.0068894 0.088 0.212 0.0069157 0.089 0.211 0.0069418 0.090 0.2100.0069677 0.091 0.209 0.0069934 0.092 0.208 0.0070189 0.093 0.2070.0070443 0.094 0.206 0.0070694 0.095 0.205 0.0070944 0.096 0.2040.0071192 0.097 0.203 0.0071439 0.098 0.202 0.0071683 0.099 0.2010.0071926 0.100 0.200 0.0072168 0.101 0.199 0.0072407 0.102 0.1980.0072646 0.103 0.197 0.0072882 0.104 0.196 0.0073117 0.105 0.1950.0073351 0.106 0.194 0.0073583 0.107 0.193 0.0073814 0.108 0.1920.0074043 0.109 0.191 0.0074271 0.110 0.190 0.0074497 0.111 0.1890.0074722 0.112 0.188 0.0074946 0.113 0.187 0.0075168 0.114 0.1860.0075390 0.115 0.185 0.0075609 0.116 0.184 0.0075828 0.117 0.1830.0076045 0.118 0.182 0.0076261 0.119 0.181 0.0076476 0.120 0.1800.0076690

As seen in FIG. 1, it is contemplated that distal end section 120 ofsurgical needle 100 includes a distal tip 122 having a profile whichdefines a tip having a sharper angle than the tip defined by thediametrical equation presented above. In particular, it is envisionedthat distal tip 122 has a uniform taper (i.e., a uniform and/or anon-parabolic surface profile). It is further contemplated that thesharper angle of distal tip 122 has a length which is substantiallyequal to one wire diameter (i.e., the diameter of the intermediate bodyportion of surgical needle).

It will be understood that various modifications may be made to theembodiments described herein. Therefore the above description should notbe construed as limiting, but merely as exemplifications of preferredembodiments. Those skilled in the art will envision other modificationswithin the scope and spirit of the claims appended hereto.

1-10. (canceled)
 11. A surgical needle, comprising: a proximal endsection configured and adapted to secure a suture thereto; a centralsection having a substantially uniform transverse cross-sectionalprofile; and a distal end section having a substantially parabolicsurface profile, the surface profile being define by the followingequation:d=(((32 W)/(nσ))*(Xn))ˆ(⅓) where d=measured diameter at location Xn;W=load normal to the needle; Xn=distance from a distal-most end of theneedle; and σ=chosen stress restraint
 12. The surgical needle of claim11, wherein the distal end section includes a distal tip having asubstantially uniform taper.
 13. The surgical needle of claim 12,wherein the distal tip has. length which the substantially equal to adiameter of the central section of the needle.
 14. The surgical needleof claim 11, wherein the central section has a cross-sectional profileconsisting essentially of a rectilinear, circular, oval, triangular,I-beam and ribbon shape.
 15. A surgical needle, comprising: A linearbody portion including: a proximal end section; a central section; and adistal end section, the distal end section having a substantiallyparabolic configuration, wherein the distal end section has a diameterdetermined according to the following equation;d=(((32 W)/(nσ))*(Xn))ˆ(⅓) where d=measured diameter at location Xn;W=load normal to the needle; Xn=distance from a distal-most end of theneedle; and σ=chosen stress restraint.
 16. The surgical needle of claim15, wherein the distal end section includes a distal tip having asubstantially uniform taper.
 17. The surgical needle of claim 16,wherein the distal tip has a length which is substantially equal to adiameter of the central section.
 18. The surgical needle of claim 15,wherein the proximal end section is configured and adapted to secure asuture thereto.
 19. The surgical needle of claim 15, wherein the centralsection has at least one of a rectilinear, circular, oval, triangular,I-beam and ribbon shaped cross-sectional profile.